Please help!

Last christmas I bought my mom a used iphone 3g which was on the fido network (canada.) My moms on the telus network, so naturally I had to jailbreak and unlock the phone for her. Everything went fine until she lost her sim card tray a month ago. I ordered a replacement one for her on amazon (this one)

and it just arrived. When we put her sim card in it, it fits a little loosely and the sim card has space to move around. When I put the sim card in the phone with the new tray, it just says "searching" or "no signal." What can I do to fix it??

During this time I plugged it into my computer to download music and that might have updated it, I'm not sure.

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